Papers by Keyword: Induction Surface Hardening

Abstract: In the present paper, a new numerical model for calculating martensite microstructure in induction surface hardening processes is introduced. It takes into account the heating as well as the quenching process and uses the temperature history of a work piece to calculate martensite formation. The calculation is based on an empirical equation found by Koistinen and Marburger [1].A comparison between the heat distribution within a work piece at the end of the heating process and the distribution of martensite after quenching is performed for different process parameters. Thus, it is determined, in which case the temperature distribution is sufficient to predict the hardened layer and in which case the microstructure has to be calculated to receive accurate results. The model is verified by comparing simulation results with different experiments.

Abstract: In this paper the microstructural and residual-stress analysis of an induction hardened plate of medium carbon steel is described. The stress gradient was determined using laboratory X-ray diffraction (IWT, Bremen, Germany) and neutron strain scanning (ILL, Grenoble, France). Due to slight variations of chemical composition in the depth, matchstick like (cross section 2×2mm²) d₀-reference samples were prepared from a similarly treated sample. The d₀ shift induced by variation of chemical composition was measured by neutron and by X-ray diffraction along the strain free direction (sin²ψ*) and used for the evaluation of the neutron stress calculation. The d₀ distribution obtained from the neutron measurement did not appear reliable while the method using X-ray diffraction seems to be an efficient and reliable method to determine d₀ profiles in small samples. The evaluation of neutron measurements was then done using the X-ray diffraction d₀ distribution. High compressive residual stresses were measured in the hardened layer followed by high tensile residual stresses in the core. A comparison of the neutron measurements with X-ray diffraction (XRD) depth profiles obtained after successive layer removal showed that both methods give similar results. However, these investigations opened the question about the direct comparison of the residual stresses obtained by neutron and XRD. Indeed, a correction of the neutron data regarding the residual stresses in thickness direction might be necessary as these are released in the case of X-ray diffraction measurements after layer removal.

Abstract: The paper deals with a novel method suitable for modelling of surface induction hardening and other tasks, where the problem of discretisation of very thin eddy-currents surface layer is present. The method is based on artificial change of material parameters in the computer model. A methodology is suggested and limitations of its application are thoroughly tested. Odds and merits over other possible methods are also discussed.

Abstract: Induction surface hardening creates very desirable residual stresses in the hardened surface layer. Residual stresses are always of a compressive nature and are usually present to the depth of the induction-hardened layer. By the appropriate selection of grinding wheel and grinding conditions and taking into account the physical and mechanical properties of the workpiece material very favourable compressive residual stresses in the hardened surface layer can be retained. How is it possible to assure a desirable surface and surface layer quality after induction hardening and fine grinding Finding an answer to this question requires a very good knowledge of the process of grinding on the micro-level as well as knowledge of mechanical and heat effects acting on the layer of the workpiece including the type and condition of the grinding wheel. An allinclusive consideration of the numerous influences of the kind and condition of the tool on the changes on the surface and in the surface layer of the workpiece in the given machining conditions is described by the term “surface integrity”.